Conventional engine cooling systems maintain normal operating temperatures irrespective of traveling conditions. A water cooling system, which is one of the cooling systems for cooling engines, basically comprises a water pump for forcibly delivering a coolant, a radiator for cooling a high-temperature coolant, and a thermostat for controlling the flow of the coolant on the basis of the temperature of the coolant.
Such a water cooled engine is typically provided with a water jacket with channels formed in a cylinder block and in a cylinder head of a conventional engine, respectively, through which the coolant flows. However, the water jacket formed in the cylinder block of the engine has a coolant inlet and a coolant outlet, which are typically formed in the same area toward the intake side of the engine. Consequently, the coolant does not uniformly flow to the vicinities of cylinder bores of the engine, whereby the cooling efficiency of the engine is very low.
In a conventional engine cooling system, the water jacket formed in the cylinder block communicates with the water jacket formed in the cylinder head, which leads to a sharing of the coolant. As a result, the coolant delivered from the water pump is supplied to the cylinder head via the cylinder block. Consequently, insufficient cooling of the cylinder head results in it having a temperature higher than that of the cylinder block as fuel in the engine is combusted.